Export types and functions needed by priroda

Remove reundant dangling checks in {r,d}eallocate

use libstd methods for floating-point <-> bytes conversion

Ensure that it is not possible to explicitly free stack memory

lvalue: refactoring to permit applying a mir projection to a miri lvalue

Re-do packed memory accesses

Get rid of magic numbers

instead read them from the `libc` crate if available.

fixes #216

Memory::read_ptr has to check for relocations on the edges

We now track in the lvalue whether what we computed is expected to be aligend or not, and then set some state in the memory system accordingly to make it (not) do alignment checks

Produce `ConstInt` from a `def_id` for rustc

Add tests for #113

resolves #113

Add little script to build libstd